Surfactants have been widely formulated in cleansing products in cosmetic applications. The major function of surfactants in rinse off products is to cleanse the skin and hair of fatty and water-soluble impurities, however, surfactants meanwhile also cause irritation.
In skin care applications, surfactants function to remove normal skin lipids. The natural water-lipid film that functions to protect the skin is disturbed with every wash. Hydrophilic groups of the negatively charged polar surfactant anions react with the weakly cationic, positively charged amino groups of proteins of the skin and mucosa. Therefore, surfactants are known for their irritancy to eyes and defatting to skin, this is especially the case for anionic surfactants, which react with proteins in the skin and mucous membranes. The similar defatting effect from surfactant is also true in hair care. The most critically assessed surfactants are sodium lauryl and laureth sulfate, which can significantly cause hair harshness after the shampooing.
Another important aspect of surfactants is their foaming properties. Consumer's perception of foam is physiologically related to the efficacy of cleansing. The products that generate large volume and size of foam during application are often perceived to have better a cleansing effect. The typical surfactants of fatty alcohol sulfates generate good amounts of foam with medium to large foam bubble sizes.
In both hair care and skin care applications, many polymeric conditioners and emollients are inherently hydrophobic and they tend to be difficult to be spread and can leave deposits left on skin or hair if the formulation has poor wetting properties. Therefore, wetting is another important property to be assessed. Surface tension is used as one of the tools for the evaluation of wetting property. Common surfactants, e.g. fatty alcohol sulfates, have low surface tension, which helps to enhance the wetting attribute in formulations for hair and skin.
One major concern for surfactants is their irritancy. Many studies have been done over the decades to reduce the irritancy and defatting disadvantages of surfactants. However, over the course of the development of low irritancy surfactants, scientists often have a dilemma: in exchange for low irritancy the foam property was sacrificed.
An alternative surfactant to fatty alcohol sulfates is therefore desired.